Double piston engine

ABSTRACT

A cylinder separated into two opposed portions interconnected by an elongated gas passageway which is constantly heated at one end and constantly cooled at its opposite end. Gas is forced back and forth through the passageway by a free piston arranged within the cylinder portion between the heated passageway end and adjacent cylinder end and by a driven piston arranged in the opposite cylinder portion. The free piston is reciprocated by the pressure of the heated gas on one face and the pressure on its opposite fact of gas compressed by the free piston itself. The driven piston is connected to a power takeoff shaft and is reciprocated on its drive stroke by the pressure of the cooled gas from the passageway and on its return stroke by a mechanical means, such as a flywheel, aided by reduced gas pressure against the driven piston.

United States Patent Primary Examiner-Martin P. Schwadron AssistantExaminer-Allen M. Ostrager Attorney-Cullen, Sloman & Cantor ABSTRACT: Acylinder separated into two opposed portions interconnected by anelongated gas passageway which is constantly heated at one end andconstantly cooled at its opposite end. Gas is forced back and forththrough the passageway by a free piston arranged within the cylinderportion between the heated passageway end and adjacent cylinder end andby a driven piston arranged in the opposite cylinder portion. The freepiston is reciprocated by the pressure of the heated gas on one face andthe pressure on its opposite fact of gas compressed by the free pistonitself. The driven piston is connected to a power takeoff shaft and isreciprocated on its drive stroke by the pressure of the cooled gas fromthe passageway and on its return stroke by a mechanical means, such as aflywheel, aided by reduced gas pressure against the driven piston.

PATENIED JUN 8191: 3583155 MARK SCHUMAN BY h fi ATTORNEYS PATENTEU JUN 8IBM SHEET 3 [1F 4 FIGS FIGB

INVENTOR MARK SCHUMAN ATTORNEYS DOUBLE PISTON ENGINE BACKGROUND OFINVENTION This invention relates to a pistontype engine of the typeutilizing an external heat source for providing heated gas within thecylinder. In the past, such engines typically utilized a heated gas suchas steam, fed into the engine cylinder to move a drive piston coupled toa power takeoff shaft.

At times, such engines have included a pair of pistons, both coupled totakeoff power shafts or have utilized one or two free pistons withsuitable mechanisms for power takeoff.

Such prior engines have been relatively expensive and inefficient andtypically have included discharging the heated gases from the cylinderafter the drive stroke, then con densing, pumping, heating and returningthe gas at high pressure to the cylinder. This is contrasted with theengine herein which is adapted for recycling a gaseous mixturesubstantially within the cylinder, and at the piston frequency.

SUMMARY OF INVENTION Summarizing, the invention herein contemplatescombining a free piston with a driven piston within the same cylinder,utilizing a recycled gas or vapor which is heated from external sourcesand is also cooled from external sources in order to provide maximumoperating efficiency and economy and overall clean operation.

More specifically, the invention contemplates providing a free piston atone'end of the cylinder, a driven piston coupled to a power takeoff atthe opposite end, with the two cylinder portions being interconnected byelongated gas passageways which are externally heated at the free pistonend and cooled at the driven piston end for movement of heated andcooled gas respectively into the opposite cylinder ends for driving thedriven and free pistons. The free piston is constantly oscillated andits oscillation or reciprocation is controlled for controlling the poweroutput of the engine.

These and other objects and advantages of this invention will becomeapparent upon reading the following description of which the attacheddrawings form a part.

DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectional elevational viewschematically showing the engine herein.

FIG. 2 is a cross-sectional view taken in the direction of arrows 2-2 ofFIG. 1.

FIG. 3 is an enlarged, fragmentary view of a portion of a piston and thecylinder wall.

FIG. 4 is an end view ofthe free piston.

FIG. 5 is a cross-sectional view taken in the direction of arrows 5-5 ofFIG. 1.

FIGS. 6 through 9, inclusive, show steps in the operating cycle of theengine for one particular set of valve adjustments.

FIG. 10 is a view similar to FIG. 1, but showing a modifica tion.

DETAILED DESCRIPTION The engine 10 is formed of an elongated, closedcylinder 11 containing a free piston 12 at one end and a driven piston13 near the opposite end. The driven piston is connected by a pivot 14to a connecting rod 15 in turn connected to a suitable flywheel 16 towhich the power output shaft 17 is connected.

The middle of the cylinder, between the pistons, is blocked by a tiller20 which includes a number of elongated spaced apart plates 21 eachhaving gas passageways 22 extending therethrough. The plates are spacedapart and the gaps between them are blocked by end spacers 23 located attheir upper and lower ends. Central spacers 24 divide the gaps betweenthe plates into upper heating spaces 25 and lower cooling spaces 26.

Referring to FIG. 2, a suitable heat source 37 illustrated schematicallyas coils is connected by a heated fluid inlet 28 and outlet 29 into eachof the upper heating spaces 25. The

purpose is to heat the upper ends of the passageways by heating theplates near their upper ends. Such heating means, for example, could bein the form ofa fossil-fueled heater, heating a liquid circulatedthrough the inlet 28, the heating spaces 25 and the outlet 29.Alternatively, coils could be placed within the heating spaces 25 forheating the upper ends of the plates and conveying fluid which has beenheated. The particular form of heater may vary depending upon cost,availability and efficiency. For example, in some places a solar heaterwould be more economical whereas in other places an electrical typeheater might be more economical.

Similarly, a cooling source 30, also schematically shown as coils,provides cooling liquid into the lower cooling spaces 26 through inlets31 and out outlets 32. Any suitable and conventional cooling means canbe used such as a refrigerating apparatus, cooled water in an availablepool or body of water, air cooling, etc.

It is desirable to provide the maximum difference in temperature inheating source and cooling source, consistent with economies, and toprovide substantially constant or uniform heat and cooling at the upperand lower ends of the passageways respectively, for a given poweroutput.

Preferably, both the free piston 12 and the driven piston 13 are hollowwith their exterior piston walls 35 being formed of a gas perviousmaterial, such as sintered metals through which gas may leak. Thus, agas bearing is formed between the walls of the pistons and the cylinderwall to avoid piston-cylinder contact and wear. Each piston is providedwith a piston check valve 36 for receiving gas on its compressionstroke, which in the case of the free piston is the bottom of its strokeand in the case of the driven piston is the top of its stroke. The checkvalves otherwise are closed.

In addition, the opposing faces of each of the pistons are bent orotherwise formed into V-shaped or sawtoothlike fins. The end spacers 23are correspondingly formed into mating or interfitting fins for meshingwith the fins of the pistons and thereby considerably increasing thespeed of heat transfer and the percentage of gas moved between theopposed faces of the pistons, and therefore the ultimate efficiency ofthe engine.

A pressurized surge tank 40 is provided outside of the cylinder and isconnected by a pipe 411 to the space 42 above the free piston through anadjustable, spring-loaded throttle valve 43 of conventionalconstruction. The tank is likewise connected through a pipe 44 to thespace 45 below the free piston, through a similar throttle valve 46.

In addition, the surge tank 40 is also connected by a pipe 47 to thespace 48 above the driven piston 13, again through the same type ofthrottle valve 49.

A bypass or shunt pipe 51 connects the space 48 above the driven pistonto the cylinder portion beneath the driven piston, with a spring-loadedthrottle valve 52 for adjusting the pressure of the gas above the drivenpiston. This affects the amount of gas undergoing the temperature cycleand thus the rate of converting thermal energy into mechanical energy.This may also be affected by the other throttle valves.

OPERATION The general operation of the engine is as follows: The freepiston 12 reciprocates upwardly and downwardly, being driven upwards bythe upward movement of the driven piston and the heating of the gascoming from space 45. As the free piston moves upwards it compresses thegas above it and below the top of the cylinder to the point where thatcompressed gas serves to drive the piston back downwardly again. Thus,in effect, the free piston is simply bounced up and down by the heated,compressed gas below it and by the gas which it itself has compressedabove it. By adjusting the throttle valves 43 and 46, the stroke of thefree piston is controlled, particularly as to amplitude by controllingthe pressure from the pressurized surge tank. The surge tank pressuremay be adjusted by the throttle valve 49.

On the downstroke of the free piston, the gas, due to the downwardmovement of the pistons and the heating from heating spaces 25, ispushed and expands downwardly, at high pressure, into the space 48 abovethe driven piston which thereby drives the driven piston downwardly. Thedriven piston returns upwardly by the inertia of the flywheel 16 or bysome other suitable mechanical mechanism, as is conventional in engines,and aided by the drop in pressure caused by cooling of the gas due tocooling spaces 26.

As can be seen, the gas reaching the finned face of the free pistonis'heated. When the gas is driven downwardly towards the driven piston,it is cooled at the lower ends of the passageways 22, thereby reducingthe pressure between the pistons during the upstroke of the drivenpiston and increasing the pressure during the downstroke of the drivenpiston.

The two pistons generally are timed to operate on the same cycle ofmovements upwardly and downwardly, but normally the free piston will lagthe driven piston some predetermined amount of the cycle, such as byone-quarter cycle.

FIGS. 6 through 9 illustrate successive steps in a single cycle ofengine operation. FIG. 6 shows the driven piston 13, threequarters ofthe way up on its upstroke. The free piston, lagging the driven pistonby about one-quarter cycle is halfway up on its upstroke. Gas (shown byarrows) is being forced upwardly through the passageways 22 into thespace below the free piston 12, the gas being heated near the tops ofthe passageways.

At this portion of the cycle, the throttle valves 43, 46 and 49 areclosed as is the check valve 52.

In FIG. 7, the driven piston 13 is one-quarter way down on itsdownstroke, while the free piston I2 is at its top dead center. At thispoint, the gas from the space 45 beneath the free piston is justbeginning to flow back into the passageways 22 and downwardly. At thispoint, throttle valve 46 is cracked open by its spring loading and someof the gas from space 45 flows into the surge tank 40, which in thisexample, is kept at a relatively low pressure.

In FIG. 8, the driven piston 13 is three-quarters of the way down on itsdownstroke and the free piston is halfway down on its downstroke. Now,the gas is freely flowing from the space 45 beneath the free pistonthrough the passageways and into the space 48 above the driven piston,the gas being cooled as it passes through the lower ends of thepassageways.

Here, the throttle valve 49 is open for flow of gas from the surge tankinto the space 48 above the driven piston. Simultaneously, the throttlevalve 52 has opened to permit gas to recharge the space 48 above thedriven piston to the desired minimum pressure.

FIG. 9 shows the driven piston again on its upstroke, about one-quarterof the way up with the free piston at its bottom dead center. Thepistons are so formed that they do not actually make contacts with themating fins but simply closely approach them and this is done by properdimensioning of the connecting rod 15 as well as by the pressure in thefree piston end ofthe cylinder.

Here, the gas is now beginning to flow upwardly again. Throttle valve 43is opened by means of its spring loading to permit gas flow as shown bythe arrows. The throttle valves 49 and 52 are about to close. Cooling ofthe gas in the space 48 reduces the pressure on the driven piston duringits upstroke.

The cycle repeats itself in the usual engine fashion in the manner asdescribed above,

A higher pressure stored in the surge tank 40 and applied by means ofvalves 43 and 46 to the gas trapped in spaces 42 and 45, above and belowthe free piston, would affect the amplitude of oscillation of the freepiston, the amount of gas undergoing the temperature cycle andtherefore, the power output.

A change in the pressure of gas trapped in space 42 relative to thattrapped in space 45 will cause an upward or downward shift in the meanposition of the free piston, and likewise will affect the power output.

MODIFICATION FIG. 10

FIG. 10 illustrates a modification substantially the same as that shownin FIG. 1. However, in FIG. 10, the bypass pipe 51 and check valve 52have been replaced by a bypass pipe 60 which leads from the space belowdriven piston 13 to a throttle valve 61 and pipe 62 into the space 48above the driven piston. In addition, a pipe 63 connects space 42, abovethe free piston 12, through a check valve 64 (shown schematically) to adome 65 formed on the upper end of the cylinder. That dome receives adomed portion 66 formed on the upper end ofthe free piston 12.

Another pipe 71 communicates through a check valve 67 and a passageway68 formed in modified outer vane 69 into the space 70 formed in the freepiston.

With this construction, trapped gas in the dome 65 and in the space 70in the free piston is compressed during the respective up and downmovement of the free piston to prevent any possibility of the pistonbottoming against the cylinder on its upward stroke or against the finson the downward stroke.

The throttle valve 61 may also serve for adjusting the average pressurein the entire portion of the apparatus above the driven piston andthereby, may serve as an additional power control.

Also added to the apparatus is an additional surge tank connectedthrough a throttle valve 81 to the pipe 47 which communicates with thespace 48 above the driven piston. The surge tank 80 also is connected toanother throttle valve 82 communicating through a passage 83 into thespace 84 located between the outer vanes,just above the driven piston.The throttle valve 81 and 82 are spring loaded for presetting to apredetermined pressure.

Valve 81 serves to store a chosen pressure in the surge tank 80. For apower change in the system, valve 82 opens during a portion of thestroke to apply the stored pressure from surge tank 80 into the centralregion or space 84 for changing the pressure in the region between thetwo pistons.

For example, valve 81 may be normally closed, with its valve wafer downand seated, but opening at the maximum pressure when the driven pistonis three-quarters of the way up on its upstroke. The valve 81 may thenclose when the piston is three-quarters on the way down on a valvestroke.

Valve 82 is normally closed, but may be adjusted to open at the maximumcylinder pressure, when driven piston 13 is onequarter of the way downon its downstroke, to release stored pressure into the area 84 toincrease the drive pressure against the driven piston.

As can be seen, these additions to the basic system described in FIG. 1,provides for more flexibility and better control of the operation.

Having fully described an operative embodiment of this invention, I nowclaim:

1. An engine comprising a closed free piston cylinder portion containinga reciprocating free piston having opposite piston faces, and a drivenpiston cylinder portion containing a reciprocating driven piston;

the two cylinder portions being interconnected by an elongated gaspassageway extending within the cylinder for conveying gas into andbetween them, with the two pistons reciprocating towards and away fromtheir adjacent passageway ends so that each forces gas through thepassageway towards the other;

means for constantly heating the passageway adjacent to the free pistoncylinder portion, and means for constantly cooling the passagewayadjacent to the driven piston cylinder portion for respectively heatingand cooling the gas passing through the passageway;

the free piston being alternately reciprocated by the pressure of theheated gas, received in its cylinder portion from the passageway,applied against one face thereof and by the pressure of gas compressedbetween its opposite face and the adjacent end of the piston portion;

and the driven piston being alternately reciprocated by the pressure ofthe cooled gas received from its adjacent passageway end and by a meansfor reciprocating the driven piston back towards its passageway end.

2. An engine as defined in claim 1, and said cylinder portions beingformed of the opposite end portions of a single cylinder, the pistonsreciprocating towards and away from each other, with means blocking thecentral portion of the cylinder between the pistons, except for saidpassageway.

3. An engine as defined in claim 2, and said blocking means includingelongated plates extending between the pistons, each having gaspassageways extending to the cylinder end portions between the opposedpiston faces.

4. An engine as defined in claim 3, and with the opposed piston faceseach being formed into an axially elongated, sawtoothlike finconfiguration, and correspondingly shaped fins formed on the blockingmeans between the plates and extending between and mating with theiradjacent piston face fins.

S. An engine as defined in claim 1, and including a source of compressedgases connected through a throttle valve to the free piston cylinderportion at each of the opposite ends ofthe free piston for controllingthe pressure ofthe gas upon the opposite faces of the free piston andtherefor the stroke of the free piston.

6. An engine comprising a closed cylinder having a free piston in oneend and a driven pistonl coupled to a power takeoff means in itsopposite end, with the pistons being reciprocally fitted within thecylinder and with the two piston containing cylinder ends connected byat least one elongated passageway extending within the cylinder throughwhich gas may freely pass to the opposed faces of the two pistons;

means for externally, constantly heating the passageway at the freepiston end thereof and for externally, constantly cooling the passagewayat the driven piston end thereof for thereby respectively heating andcooling gas moved through the passageway by reciprocation ofthe pistons.

7. An engine as defined in claim 6 above, and said passageway beingformed lengthwise through an elongated plate extending between thepistons .and fixed within the cylinder, the cylinder being blockedagainst movement of gas between the pistons except for the passageway;and said heating and cooling means being applied to the upper and lowerend portions, respectively, of the plate.

8. An engine as defined by claim 6 above and with the opposing faces ofthe two pistons each being formed in a sawtoothlike fin configuration;and means blocking the cylinder between the piston opposing faces exceptfor the passageway, said means including sawtoothlike fins arranged forfitting between and mating with the adjacent piston fins.

1. An engine comprising a closed free piston cylinder portion containinga reciprocating free piston having opposite piston faces, and a drivenpiston cylinder portion containing a reciprocating driven piston; thetwo cylinder portions being interconnected by an elongated gaspassageway extending within the cylinder for conveying gas into andbetween them, with the two pistons reciprocating towards and away fromtheir adjacent passageway ends so that each forces gas through thepassageway towards the other; means for constantly heating thepassageway adjacent to the free piston cylinder portion, and means forconstantly cooling the passageway adjacent to the driven piston cylinderportion for respectively heating and cooling the gas passing through thepassageway; the free piston being alternately reciprocated by thepressure of the heated gas, received in its cylinder portion from thepassageway, applied against one face thereof and by the pressure of gascompressed between its opposite face and the adjacent end of the pistonportion; and the driven piston being alternately reciprocated by thepressure of the cooled gas received from its adjacent passageway end andby a means for reciprocating the driven piston back towards itspassageway end.
 2. An engine as defined in claim 1, and said cylinderportions being formed of the opposite end portions of a single cylinder,the pistons reciprocating towards and away from each other, with meansblocking the central portion of the cylinder between the pistons, exceptfor said passageway.
 3. An engine as defined in claim 2, and saidblocking means including elongated plates extending between the pistons,each having gas passageways extending to the cylinder end portionsbetween the opposed piston faces.
 4. An engine as defined in claim 3,and with the opposed piston faces each being formed into an axiallyelongated, sawtoothlike fin configuration, and correspondingly shapedfins formed on the blocking means between the plates and extendingbetween and mating with their adjacent piston face fins.
 5. An engine asdefined in claim 1, and including a source of compressed gases connectedthrough a throttle valve to the free piston cylinder portion at each ofthe opposite ends of the free piston for controlling the pressure of thegas upon the opposite faces of the free piston and therefor the strokeof the free piston.
 6. An engine comprising a closed cylinder having afree piston in one end and a driven piston coupled to a power takeoffmeans in its opposite end, with the pistons being reciprocally fittedwithin the cylinder and with the two piston containing cylinder endsconnected by at least one elongated passageway extending within thecylinder through which gas may freely pass to the opposed faces of thetwo pistons; means for externally, constantly heating the passageway atthe free piston end thereof and for externally, constantly cooling thepassageway at the driven piston end thereof for thereby respectivelyheating and cooling gas moved through the passageway by reciprocation ofthe pistons.
 7. An engine as defined in claim 6 above, and saidpassageway being formed lengthwise through an elongated plate extendingbetween the pistons and fixed within the cylinder, the cylinder beingblocked against movement of gas between the pistons except for thepassageway; and said heating and cooling means being applied to theupper and lower end portions, respectively, of the plate.
 8. An engineas defined by claim 6 above and with the opposing faces of the twopistons each being formed in a sawtoothlike fin configuration; and meansblocking the cylinder between the piston opposing faces except for thepassageway, said means including sawtoothlike fins arranged for fittingbetween and mating with the adjacent piston fins.